Positive Electrode Materials Having a Superior Hardness Strength

ABSTRACT

A powderous positive electrode material for a lithium secondary battery, the material having the general formula Li 1 +x[Ni1−a−b−cMaM′bM″c] 1−xO2−z; M being either one or more elements of the group Mn, Zr and Ti, M′ being either one or more elements of the group Al, B and Co, M″ being a dopant different from M and M′, x, a, b and c being expressed in mol with −0.02≦x≦0.02, 0≦c≦0.05, 0.10≦(a+b)≦0.65 and 0≦z≦0.05; and wherein the powderous material is characterized by having a BET value ≦0.37 m 2 /g, a Dmax&lt;50 μm, and a hardness strength index ΔΓ(P) of no more than 100%+(1−2a−b)×160% for P=200 MPa, wherein (Formula I) (I) with D 10p=0 being the D10 value of the unconstrained powder (P=0 M Pa), r°(D 10p=0) being the cumulative volume particle size distribution of the unconstrained powder at D 10p=0, and Γ p (D 10p=0) being the cumulative volume particle size distribution at D10p=0 of the pressed samples with P being expressed in M Pa.

TECHNICAL FIELD AND BACKGROUND

This invention relates to metal oxide compounds and to preparationmethods thereof. More specifically, this invention relates to dopedmetal oxide insertion compounds for use in lithium and lithium-ionbatteries.

In recent years, secondary lithium ion batteries superseded otherbattery systems due to their relatively high gravimetric and volumetricenergy density. These features are particularly desirable to accompanythe miniaturization of portable electronics (such as laptops,smartphones or cameras . . . ) and foreseen as suitable for electricalvehicles (HEV or EV) with long operational range. The latter applicationrequires batteries able to sustain good charge-discharge cycle lifeunder real operating conditions, namely several thousand of cycles atover an extended temperature range and high rate of discharge. Themajority of rechargeable lithium ion batteries use anode materials whichdo not contain lithium metal, for example carbon and/or metal alloy(such as silicon alloys, tin alloys . . . ) containing materials. Thecathode must then contain lithium which can be reversibly extractedduring charge and inserted during discharge in order to deliver goodcycle life.

Most promising materials as cathodes for rechargeable lithium ionbatteries are lithium transition metal oxides with a layered structurederived from α-NaFeO₂ (space group R-3m). Since the introduction of thefirst Li-ion battery in 1990 by Sony into consumer electronics; LiCoO₂is still the most commonly used cathode materials thanks to its goodcycle life, very high pressed density—commonly exceeding 3.7 g/cm³—andlarge specific capacity of about 140 mAh/g at 4.2V against graphiteanodes. LiCoO₂ is however less favored by its very high and fluctuatingprice and relative scarcity of cobalt, which limits its use for theemerging EV mass-market. Alternative cathode active materials such asLiNiO₂ have been investigated due to larger availability and lower priceof nickel. LiNiO₂ also features a higher specific capacity when comparedto LiCoO₂; typically exceeding 200 mAh/g at 4.2V, due to the lowerpotential of the transition metal oxide redox-couple. LiNiO₂ has twoshortcomings:

-   -   (i) LiNiO₂ raises safety concerns because it has a sharper        exothermic reaction with electrolyte at a lower temperature than        LiCoO₂, as evidenced by DSC (see Dahn et al, Solid State Ionics,        69, 265 (1994)), ultimately leading to thermal runaway and        catastrophic failure of the battery. Accordingly, pure LiNiO₂ is        generally not selected for use in commercial lithium-ion        batteries.    -   (ii) Higher specific capacity at a given cell voltage means that        larger amounts of Li can be reversibly de-intercalated per unit        of LiNiO₂, leading to significant changes of the crystal volume        upon charge and discharge cycling. Such repeated large        variations of the crystal volume can lead to cathode materials'        primary and secondary particles not being able to sustain such        stress. Particle fracture and loss of electrical contact may        occur within the electrode and this ultimately impairs the cycle        life of the Li-ion battery.

For improving the abovementioned issues, especially the ones related tosafety for LiNiO₂, various doping elements have been introduced, forexample electrochemically inactive ions such as Mg²⁺, Ti⁴⁺ and Al³⁺ (seefor example U.S. Pat. No. 6,794,085 B2). Such a doping strategy howeverfrequently results in a decrease of specific capacity and lower power inreal cells, and is not preferred for the end application.

A more promising route is Co and Mn substitution of Ni (as disclosed inUS 2003/0022063 A1) leading to a so called NMC-type composition with theidealized general formula Li_(1+x)[Ni_(1-a-b)Mn_(a)Co_(b)]_(1−x)O₂. Thisidealized formula doesn't expressly take into account cation mixing,which is the ability of a metal, generally nickel in divalent state, tooccupy sites in the lithium layers. It is generally admitted that Mn istetravalent, Co trivalent and Ni bears a 2+/3+ charge. It is trivial toshow that the fraction of nickel ions being effectively Ni³⁺ is:

$\frac{\left( {\frac{1 + x}{1 - x} - {2a} - b} \right)}{1 - a - b}\mspace{14mu} {where}\mspace{14mu} \frac{1 + x}{1 - x}$

is referred to as the lithium to metal molar ratio.

The Ni³⁺ molar content is therefore equal to:

$\left( {\frac{1 + x}{1 - x} - {2a} - b} \right) \times {\left( {1 - x} \right).}$

When Li:M is close to 1, meaning that for x˜0 (or −0.05≦x≦0.05), theNi³⁺ molar content is approximates 1−2a−b. This last expression will beconsidered to calculate the effective Ni³⁺ content in the followingexamples with the convention that “a” represents tetravalent metalcations (examples include—but are not limited to—Mn⁴⁺, Zr⁴⁺ or Ti⁴⁺),and b represents trivalent metal cations (examples include—but are notlimited to—Co³⁺ and Al³⁺). Likewise, the calculation of effective Ni³⁺fraction can be extended to take into account divalent metal cationdoping such as Mg²⁺and Ca²⁺; one can show that the content is given by(1−2a−b)/(1−a−b−c) where c represents the molar content of divalentcations.

In these NMC materials, the specific capacity, hence the amount of Lireversibly de-intercalating from the materials, increases when theeffective Ni³⁺ content increases. For example, popular compositions suchas 111 (111 standing for the molar ratio of Ni:Mn:Co, with ˜0.1 moleNi³⁺ per mole of product), 532 (˜0.2 mole Ni³⁺), 622 (˜0.4 mole Ni³⁺)and 811 (˜0.7 mole Ni³⁺) typically have a specific discharge capacity of150, 160, 170 and 190 mAh/g, respectively, when cycled between 4.2 and2.7V against a graphite anode.

More lithium ions are then reversibly extracted from the materials,resulting in a higher particle strain when the effective Ni³⁺ content isincreased. Strain ultimately will lead to particle fracture andelectrode degradation, hence accelerating the rate of capacity fadingand impairing the cycle life of the cell. In addition, such particlefracture creates new exposed surfaces which will eventually accelerateside reactions on the cathode, namely electrolyte oxidation, and furtherreduce the cycle life of the battery. Such issues become more criticalfor systems requiring a higher power output: typically modern EVapplications require operating C-rates superior to 1 C and even up to 5C (1 C=1 h and 5 C=12 mins to complete full battery charging ordischarging). Cathode materials must be able to accommodate straingenerated by volume change of the unit cell due to insertion andextraction of Li ions in a short amount of time. Clearly, it isdifficult to design materials being both able to deliver a largespecific capacity (i.e. having high effective Ni³⁺) and able toaccommodate larger strain, especially at higher power. It is the objectof the present invention to provide such materials.

The volumetric energy density (in Wh/L) of the Li-ion battery is notonly influenced by the specific discharge capacity (in mAh/g) of boththe anode and cathode electrodes, but also by the gravimetric density ofthe electrodes (in g/cm³). On the cathode side, the electrodegravimetric density is determined by:

-   -   (i) the intrinsic properties of the cathode materials such as        tap density (TD) or pressed density, and,    -   (ii) the electrode production process, for example during the        calendaring or pressing step to increase electrode density. In        such a step, an uniaxial stress is applied to the electrode in        order to reach the desired level of density (or porosity) to        achieve a high volumetric energy.

The present invention aims at providing a cathode material able tosustain such stress, id est a material with secondary particles that donot break under pressure during the manufacturing process and that areable to sustain repeated charge-discharge cycles without breaking.

In this respect, US 2004/023113 A1 is concerned with the determinationof the compressed density and compressive strength of cathode powders;the examples being mostly about LiCoO₂. In the determination of thecompressed density, the power is compressed under a pressure of 29.4MPa. Such pressure is about 10-fold lower in comparison to the presentstate of the art requirements of electrode making and is notrepresentative of the behavior of cathode materials during such process.

It is known that the particular morphology of LiCoO₂, with very dense,non-agglomerated potato-shaped particles, can sustain very highcompression stress without breaking. Composite lithium nickel manganesecobalt oxides (NMC) have a very different morphology of secondaryparticles made of agglomeration of primary particles. Such secondaryparticles are more brittle due to the occurrence of inter-particle grainboundaries which are preferred fracture points. Impurities such asun-reacted alkali salts (hydroxides, carbonates, sulfates . . . )accumulate at the grain boundaries. When the full cell is operated atpotentials above 4V, these unreacted salts decompose and dissolve in theelectrolyte, leaving the grain boundary opened and unfilled, whichdramatically impairs the mechanical resistance of the secondaryparticles. Materials comprising an excessive amount of such Li-saltimpurities demonstrate a lower resistance to mechanical stress resultingfrom electrode processing, and have an inferior tolerance to accommodatestrain resulting for Li insertion and extraction when operated in abattery at high power (=at a high discharge C-rate). It is commonlyaccepted that the higher the effective Ni³⁺ content, the moreimpurities, primarily LiOH and Li₂CO₃, accumulate at the grainboundaries, further increasing the propensity of secondary particles tobreak.

US 2009/0314985 A1 describes the compressive strength of cathode powdersand introduces the concept that the D10 value of the particle sizedistribution should changes by no more than 1 μm after compression ofthe powder under 200 MPa. Such criterion fails to properly describe thebehavior of materials having lower D10 values; especially when D10<1 μm.The only example describes the behavior of a D50=10 μm NMC 111 with +/−5mol % of Ni³⁺. Because of its low effective Ni³⁺ content NMC 111 is oneof the less brittle NMC materials. Materials having a larger effectiveNi³⁺ content—and a larger specific capacity—while keeping relatively lowsecondary particle brittleness are desirable for modern applications. Inaddition, the manufacturing process disclosed in US 2009/0314985 A1 isnot realistic for mass production: it is for example described to useoxygen gas streams and multiple step firing resulting in both high costand low throughput. In addition, no mention is made on the cycle lifeimprovement of cathode materials featuring an improved hardnessstrength.

SUMMARY

Viewed from a first aspect, the invention can provide a powderouspositive electrode material for a lithium secondary battery, thematerial having the general formulaLi_(1+x)[Ni_(1-a-b-c)M_(a)M′_(b)M″_(c)]_(1−x)O_(2-z);

M being either one or more elements of the group Mn, Zr and Ti,

M′ being either one or more elements of the group Al, B and Co,

M″ being a dopant different from M and M′,

x, a, b and c being expressed in mol with −0.02≦x≦0.02, 0≦c≦0.05,0.10≦(a+b)≦0.65 and 0≦z≦0.05; and wherein the powderous material ischaracterized by having a BET value ≦0.37 m²/g, a D_(max)<50 μm, andwherein the powderous material is characterized by having a hardnessstrength index (HSI)ΔΓ(P) value of no more than 100%+(1−2a−b)×160% forP=200 MPa, wherein

${{\Delta\Gamma}(P)} = {\frac{{\Gamma^{P}\left( {D\; 10_{P = 0}} \right)} - {\Gamma^{0}\left( {D\; 10_{P = 0}} \right)}}{\Gamma^{0}\left( {D\; 10_{P = 0}} \right)} \times 100\mspace{14mu} \left( {{in}\mspace{14mu} \%} \right)}$

with D10_(P=0) being the D10 value of the unconstrained powder (P=0MPa), Γ⁰(D10_(P=0)) being the cumulative volume particle sizedistribution of the unconstrained powder at D10_(P=0), andΓ^(P)(D10_(P=0)) being the cumulative volume particle size distributionat D10_(P=0) of the pressed samples with P being expressed in MPa. In anembodiment, M=Mn and M′ is either one of Al and Co. In anotherembodiment Dmax<45 μm. From the experiments below it is clear that avalue for BET of less than 0.20 m²/g is not obtained. In a moreparticular embodiment, 1−a−b≧0.5 and 1+x<1.000. Also, the material maycomprise up to 2 mol % of W, Mo, Nb, Zr, or a rare earth element. In oneembodiment, the material comprises a second phase LiN_(x′)O_(y′) with0<x′<1 and 0<y′<2, where Ma is either one or more of W, Mo, Nb, Zr andrare earth elements. Authors speculate that materials modified withproper additives or dopants can feature enhanced hardness strength andalso an improved cycle life. This is for example the case of additivesor dopants T such as W, Mo, Nb, Zr, or rare earth elements. Such Telements have the property to alloy with Li (for example Li₂ZrO₃,(Li₂O)_(n)(WO₃) with n=1, 2, 3; or Li₃NbO₄) and sometimes also withM=Co, Ni and Mn as in Li₄MWO₆ compounds. Such T-containing alloys arestable and accumulate at the grain boundary of particles; it results ina stabilization of the grain boundary offering better mechanicalresistance to stress and during repeated electrochemical cycling.

The material may have a Al₂O₃ surface coating, resulting in an aluminacontent greater than 1000 ppm, or even greater than 2000 ppm. Thecathode materials according to according to the invention may have lessthan 3000 pm F. In one embodiment, the material may have a S wt %content lower than 0.5 wt %, or lower than 0.25 wt %, or even lower than0.15 wt %.

In various embodiments the following features are provided:

ΔΓ(P)≦150+(1−2a−b)×160% for P=300 MPa, or

ΔΓ(P)≦125%+(1−2a−b)×100% for P=300 MPa, or

ΔΓ(P)≦180% for P=300 MPa, or

ΔΓ(P)≦140% for P=300 MPa, or

ΔΓ(P)≦100% for P=300 MPa.

For the powderous positive electrode material according to the invention

-   -   they may have a BET value after wash >1 m²/g, or also greater        than 1.5 m²/g,    -   they may have a pressed density greater than 3.0 g/cm³, or        greater than 3.2 g/cm³, or also greater than 3.4 g/cm³.    -   they may have a soluble base content (Li₂CO₃+LiOH)<0.8 wt %, or        Li₂CO₃ wt %+LiOH wt %<0.5 wt %, or also Li₂CO₃ wt %+LiOH wt        %<0.3 wt %.    -   they may comprise secondary particles substantially free from        porosities larger than 20 nm, or even free from porosities        larger than 10 nm, as is illustrated in FIG. 9-10.    -   they may comprise secondary particles comprising less than 20        voids larger than 20 nm or even less than 10 voids larger than        20 nm, as is illustrated in FIG. 9-10.    -   they may have a FWHM value of the (104) peak as defined by the        pseudo hexagonal lattice with R-3m space group which is greater        than 0.125 2-theta degrees, or greater than 0.140 2-theta        degrees, or even greater than 0.150 2-theta degrees.    -   they may have a FWHM value of the (015) peak as defined by the        pseudo hexagonal lattice with R-3m space group which is greater        than 0.125 2-theta degrees, or greater than 0.140 2-theta        degrees, or even greater than 0.150 2-theta degrees.    -   they may have a FWHM value of the (113) peak as defined by the        pseudo hexagonal lattice with R-3m space group which is greater        than 0.16 2-theta degrees, or greater than 0.18 2-theta degrees,        or even greater than 0.20 2-theta degrees.

The cathode materials according to the invention may have a 0.1 CEfad.≦(1−2a−b)×10%, or a 0.1 C Efad.≦(1−2a−b)×5%, or a 1 CEfad.≦(1−2a−b)×20% (see in the detailed description, part a) and c) forthe electrochemical testing experiments). The material may cycle for atleast 1000 cycles, or even at least 1500 cycles with a retained capacityabove 80% at room temperature in a full cell. The material may alsocycle for at least 900 cycles, or even at least 1500 cycles with aretained capacity above 80% at 45° C. in a full cell.

It is clear that further product embodiments according to the inventionmay be provided by combining features that are covered by the differentproduct embodiments described before.

Viewed from a second aspect, the invention may provide a powderouspositive electrode material incorporated in an electrode and having anelectrode density greater than 3.0+((1−2a−b)/2) g/cm³.

Viewed from a third aspect, the invention may provide a lithiumsecondary battery comprising a positive electrode active materialcomprising particles of lithium-transition metal oxide; a Li-freenegative electrode, a separator interposed between the positiveelectrode and the negative electrode; and a non-aqueous electrolyte,wherein the particles of the positive electrode active material have aΔΓ(P) values which is no more than (1−2a−b)×180% for P=300 MPa, or nomore than 2(1−x)(1−a−b)×140% for 300 MPa, or even less than (1−a−b)×100%at 300 MPa. In an embodiment the material has a FWHM of the (104) peakgreater than 0.16 2-theta and demonstrates at least 1000 cycles, or even1500 cycles with a retained capacity above 80% at room temperature. Inan embodiment the material has a FWHM of the (104) peak greater than0.16 2-theta and demonstrates at least 900 cycles with a retainedcapacity above 80% at 45° C.

Viewed from a fourth aspect, the invention may provide a method forpreparing a powderous positive electrode material according to theinvention, the material having the general formulaLi_(1+x)[Ni_(1-a-b-c)M_(a)M′_(b)M″_(c)]_(1−x)O_(2-z), and the methodcomprising the steps of:

-   -   providing a mixture of one or more precursor materials        comprising either one or more of Ni, M, M′ and M″, and a        precursor material comprising Li,    -   sintering the mixture at a temperature T expressed in ° C., with        (945−(248*(1−2a−b)≦T≦(985−(248*(1−2a−b)), thereby obtaining        agglomerated particles, and    -   pulverizing the agglomerated particles whereby a powder is        obtained having a BET≦0.37 m²/g and a D_(max)<50 μm. The D_(max)        or D100 value is the maximum particle size of the obtained        powder. In an embodiment Dmax<45 μm. From the experiments below        it is clear that a value for BET of less than 0.20 m²/g is not        obtained.

It should be mentioned here that US2011/193013 describes a powderouslithium transition metal oxide having a layered crystal structureLi_(1+a)M_(1−a)O_(2±b)M′_(k)S_(m) with −0.03<a<0.06, b≅0, 0≦m≦0.6, mbeing expressed in mol %, M being a transition metal compound,consisting of at least 95% of either one or more elements of the groupNi, Mn, Co and Ti; M′ being present on the surface of the powderousoxide, and consisting of either one or more elements of the group Ca,Sr, Y, La, Ce and Zr. The products having a BET value ≦0.37 m²/g havebeen fired at a too high temperature, causing an increase in porositythat leads to a decrease in hardness.

Also, US2006/233696 describes a powderous lithium transition metal oxidewith the composition Li_(x)M_(y)O₂ and prepared by solid state reactionin air from a mixed transition metal precursor and Li₂CO₃, the powderbeing practically free of Li₂CO₃ impurity. In the formulaM=M′_(1-k)A_(k), where M′=Ni_(1-a-b)(Ni_(1/2)Mn_(1/2))_(a)Co_(b) oncondition of 0.65≦a+b≦0.85 and 0.1≦b≦0.4; A is a dopant; and 0≦k≦0.05;and x+y=2 on condition of 0.95≦x≦1.05. The BET surface area of theprepared products is too high, causing a decrease in hardness.

Finally, in US2010/112447 the positive electrode active materialincludes a composite oxide containing lithium and Ni, Mn, and Co. Themolar ratio of Ni is from 0.45 to 0.65, and the molar ratio of Mn o isfrom 0.15 to 0.35. The positive electrode active material has a presseddensity under a compression of 60 MPa of 3.3 g/cm³ or more and 4.3 g/cm³or less. The positive electrode active material has a volume resistivityunder a compression of 60 MPa of 100 Ω·cm or more and less than 1000Ω·cm. The disclosed material however have a (Ni+Mn+Co):Li ratio of1:1.03 or more, or 1:0.95. This ratio is either too high or too low toallow to obtain products with the desired hardness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: evolution of the cumulative particle size distribution Γ^(P) asfunction of uni-axial stress P, for P=0, 100, 200 and 300 MPa forExample 1.

FIG. 2: enlargement of the evolution of the cumulative particle sizedistribution Γ^(P) as function of uni-axial stress P, for P=0, 100, 200and 300 MPa for Example 1 and showing the steps to determineΓ^(P)(D10_(P=0))

FIG. 3: full cell cycle life at room-temperature of EX1, EX2 and CEX1when cycled between 4.2 and 2.7V. Evolution of the retained capacity (in% of the initial discharge capacity) as a function of the cycle number(#).

FIG. 4: full cell cycle life at 45° C. of EX1, EX2 and CEX1 when cycledbetween 4.2 and 2.7V. Evolution of the retained capacity (in % of theinitial discharge capacity) as a function of the cycle number.

FIG. 5: cross-sectional SEM and SEM of secondary particles of Examples 1(a), 2 (b) and Counter Example 1 (c).

FIG. 6: full cell cycle life at room-temperature of EX3, EX4 and CEX2when cycled between 4.2 and 2.7V. Evolution of the retained capacity (in% of the initial discharge capacity) as a function of the cycle number(#).

FIG. 7: full cell cycle life at 45° C. of EX3, EX4 and CEX2 when cycledbetween 4.2 and 2.7V. Evolution of the retained capacity (in % of theinitial discharge capacity) as a function of the cycle number (#).

FIG. 8: SEM of secondary particles of Example 3 (top) and CounterExample 2 (bottom).

FIG. 9: cross-sectional SEM of secondary particles of Examples 3 (top),4 (middle) and Counter Example 2 (bottom).

FIG. 10: cross-sectional SEM and SEM of secondary particles of Examples5 (a), 6 (b) and Counter Example 7 (c).

FIG. 11: full cell cycle life at room-temperature of EX8, EX9 and EX10when cycled between 4.2 and 2.7V. Evolution of the retained capacity (in% of the initial discharge capacity) as a function of the cycle number(#).

FIG. 12: full cell cycle life at 45° C. of EX8, EX9 and EX10 when cycledbetween 4.2 and 2.7V. Evolution of the retained capacity (in % of theinitial discharge capacity) as a function of the cycle number (#).

FIG. 13: SEM of secondary particles of Examples 8 (a), 9 (b) and 10 (c).

FIG. 14: XRD pattern of Example 1 showing the diffracted intensity(counts) as function of 2-theta (degrees). The positions of 003, 104,015, 018, 110 and 113 reflections of the α-NaFeO₂ cell (space groupR-3m) are indicated.

FIG. 15: example of pseudo-Voigt decomposition of 018, 110 and 113 peaksin the 63˜70 2-theta range for Example 1. The open dots are theexperimental data I_(obs.) after KAlpha2 subtraction, the black solidline is the fitted profile I_(calc.) using 3 pseudo-Voigt functions andthe dashed line represents the (I_(obs.)−I_(calc.)) quantity.

DETAILED DESCRIPTION

This invention provides a cathode material able to sustain a largemechanical stress during electrode making and electrochemical stress inpower-demanding applications. Such cathode material has an improvedcycle life at both room temperature and 45° C. in full cells. Hence, thematerials according to the invention offer significant advantages suchas:

-   -   a state of the art electrode density that facilitates the        electrode production process: the cathode materials secondary        particles are able to sustain high uni-axial stress during        electrode manufacturing, with a substantially lower fracture and        breaking risk,    -   an increase in cycle life: the cathode materials' secondary        particles show substantially lower fracturing and breaking after        electrode manufacturing and upon electrochemical cycling at high        C-rate, and a good contact between the cathode secondary        particles, the binder, the conductive agent and the current        collector is preserved within the electrode, and,    -   an improved cycle life at elevated temperature. The BET increase        of cathode active materials able to sustain higher stress        according to the invention is minimized after electrode pressing        and due to particle breaking upon cycling, and hence this is        limiting the surface exposure where side reactions such as        electrolyte oxidation at higher voltage are occurring.

The methods for preparing the materials according to the invention aregenerally known, but it is by a proper selection of parameters such assintering temperature and Li/metal ratio in a single step cookingprocess—depending largely on the content of Ni³⁺ in the compounds—thatthe superior hardness and other characteristics may be achieved. Inpractice the sintering temperature of the cooking step is limited to(985−(248*(1−2a−b))° C., and the Li:M ratio (=(1+x)/(1−x)) is between0.98 and 1.02. A minimum sintering temperature can also be establishedas (945−(248*(1−2a−b))° C., to ensure that the reaction between theprecursors is completed. The reason for limiting the sinteringtemperature is to be found in the direct influence of that temperatureon the internal porosity of the particles. When the Li:M ratio is below0.98, there is a serious decrease in capacity, since the amount of Nithat is located in Li sites increases considerably. When the Li:M ratiois more than 1.02, the soluble base content increases, leading toproblems like serious gas generation in full cells, as is discussed inWO2012/107313.

Also important for the process is that after sintering the agglomeratedparticles are softly crushed or milled to ensure a proper hardness, and,since the milling increases the BET value, softly milling means that theBET of the milled product may be limited to ≦0.37 m²/g. As crushing andmilling may lead to a very high value for D_(max) (being the maximumparticle size), whereby the capacity is seriously hampered, the millingmay be controlled to lead to a D_(max)<50 μm.

General Description of Experiments

a) Evaluation of Electrochemical Properties in Coin Cells

Electrodes are prepared as follows: about 27.27 wt. % of active cathodematerial, 1.52 wt. % polyvinylidene fluoride polymer (KF polymer L#9305, Kureha America Inc.), 1.52 wt. % conductive carbon black (SuperP, Erachem Comilog Inc.) and 69.70 wt. % N-methyl-2-pyrrolidone (NMP)(from Sigma-Aldrich) are intimately mixed by means of high speedhomogenizers. The slurry is then spread in a thin layer (typically 100micrometer thick) on an aluminum foil by a tape-casting method. Afterevaporating the NMP solvent, the cast film is processed through aroll-press using a 40 micrometer gap. Electrodes are punched from thefilm using a circular die cutter measuring 14 mm in diameter. Theelectrodes are then dried overnight at 90° C. The electrodes aresubsequently weighed to determine the active material loading.Typically, the electrodes contain 90 wt. % active materials with anactive materials loading weight of about 17 mg (N11 mg/cm²). Theelectrodes are then put in an argon-filled glove box and assembledwithin a 2325-type coin cell body. The anode is a lithium foil having athickness of 500 micrometers (origin: Hosen); the separator is a Tonen20 MMS microporous polyethylene film. The coin cell is filled with a 1Msolution of LiPF₆ dissolved in a mixture of ethylene carbonate anddimethyl carbonate in a 1:2 volume ratio (origin: Techno Semichem Co.).

Each cell is cycled at 25° C. using Toscat-3100 computer-controlledgalvanostatic cycling stations (from Toyo). The coin cell testingschedule 1 used to evaluate EX1, EX2, EX4, EX4, CEX1 and CEX2 isdetailed in Table 8. Coin cell schedule 2 used to evaluate EX5, EX6,EX7, EX8, EX9 and EX10 is detailed in Table 9. Both schedules use a 1 Ccurrent definition of 160 mA/g and comprise 3 parts as follows:

(i) Part I is the evaluation of rate performance at 0.1 C, 0.2 C, 0.5 C,1 C, 2 C and 3 C in the 4.3˜3.0V/Li metal window range. With theexception of the 1^(st) cycle where the initial charge capacity CQ1 anddischarge capacity DQ1 are measured in constant current mode (CC), allsubsequent cycles feature a constant current-constant voltage during thecharge with an end current criterion of 0.05 C. A rest time of 30minutes for the first cycle and 10 minutes for all subsequent cycles isallowed between each charge and discharge.

The irreversible capacity Q_(irr.) is expressed in % as:Q_(Irr.)=(CQ1−DQ1)/CQ1×100(%) CQ1

The rate performance at 0.2 C, 0.5 C, 1 C, 2 C and 3 C is expressed asthe ratio between the retained discharge capacity DQn, with n=2, 3, 4, 5and 6 for respectively nC=0.2 C, 0.5 C, 1 C, 2 C and 3 C as follows:

${{{nC} - {rate}} = {\frac{DQn}{{DQ}\; 1} \times 100\%}},$

e.g. 3 C-rate (in %)=(DQ₆/DQ₁)×100.

(ii) Part II is the evaluation of cycle life at 1 C. Coin cell schedules1 and 2 only differ in the charge cutoff voltage, being 4.5V and 4.3V/Limetal for schedules 1 and 2 respectively. The discharge capacity at4.5V/Li metal is measured at 0.1 C at cycle 7 and 1 C at cycle 8.Capacity fadings at 0.1 C and 1 C are calculated as follows and areexpressed in % per 100 cycles:

${{0.1C\mspace{14mu} {{QFad}.}} = {\left( {1 - \frac{{DQ}\; 34}{{CQ}\; 7}} \right) \times \frac{10000}{27}\mspace{14mu} {in}\mspace{14mu} {\%/100}\mspace{14mu} {cycles}}},{{1C\mspace{14mu} {{QFad}.}} = {\left( {1 - \frac{{DQ}\; 35}{{CQ}\; 7}} \right) \times \frac{10000}{27}\mspace{14mu} {in}\mspace{14mu} {\%/100}\mspace{14mu} {{cycles}.}}}$

Energy fadings at 0.1 C and 1 C are calculated as follows and areexpressed in % per 100 cycles. Vn is the average voltage at cycle n.

${{0.1C\mspace{14mu} {{EFad}.}} = {\left( {1 - \frac{{DQ}\; 34 \times \overset{\_}{V\; 34}}{{CQ}\; 7 \times \overset{\_}{V\; 7}}} \right) \times \frac{10000}{27}\mspace{14mu} {in}\mspace{14mu} {\%/100}\mspace{14mu} {cycles}}},\text{}{{1C\mspace{14mu} {{EFad}.}} = {\left( {1 - \frac{{DQ}\; 35 \times \overset{\_}{V\; 35}}{{CQ}\; 7 \times \overset{\_}{V\; 7}}} \right) \times \frac{10000}{27}\mspace{14mu} {in}\mspace{14mu} {\%/100}\mspace{14mu} {{cycles}.}}}$

(iii) Part III is an accelerated cycle life experiment using 1 C-ratefor the charge and 1 C rate for the discharge between 4.5 and 3.0V/Limetal. Capacity and energy fading are calculated as follows:

${{1{C/1}C\mspace{14mu} {{QFad}.}} = {\left( {1 - \frac{{DQ}\; 60}{{CQ}\; 36}} \right) \times \frac{10000}{27}\mspace{14mu} {in}\mspace{14mu} {\%/100}\mspace{14mu} {cycles}}},{{1{C/1}C\mspace{14mu} {{EFad}.}} = {\left( {1 - \frac{{DQ}\; 60 \times \overset{\_}{V\; 60}}{{CQ}\; 36 \times \overset{\_}{V\; 36}}} \right) \times \frac{10000}{27}\mspace{14mu} {in}\mspace{14mu} {\%/100}\mspace{14mu} {cycles}}},$

b) Full Cell Manufacturing

650 mAh pouch-type cells are prepared as follows: the positive electrodeactive material powder is prepared as described above, Super-P (Super-P™Li commercially available from Timcal), and graphite (KS-6 commerciallyavailable from Timcal) as positive electrode conductive agents andpolyvinylidene fluoride (PVdF 1710 commercially available from Kureha)as a positive electrode binder are added to NMP (N-methyl-2-pyrrolidone)as a dispersion medium so that the mass ratio of the positive electrodeactive material powder, the positive electrode conductive agent, and thepositive electrode binder is set at 92/3/1/4. Thereafter, the mixture iskneaded to prepare a positive electrode mixture slurry. The resultingpositive electrode mixture slurry is then applied onto both sides of apositive electrode current collector, made of a 15 μm thick aluminumfoil. The width of the applied area is 43 mm and the length is 450 mm.Typical cathode active material loading weight is 13.9 mg/cm². Theelectrode is then dried and calendared using a pressure of 100 Kgf.Typical electrode density is 3.2 g/cm³. In addition, an aluminum plateserving as a positive electrode current collector tab is arc-welded toan end portion of the positive electrode.

Commercially available negative electrodes are used. In short, a mixtureof graphite, CMC (carboxy-methyl-cellulose-sodium) and SBR(styrene-butadiene-rubber), in a mass ratio of 96/2/2, is applied onboth sides of a copper foil. A nickel plate serving as a negativeelectrode current collector tab is arc-welded to an end portion of thenegative electrode. Typical cathode and anode discharge capacity ratioused for cell balancing is 0.75. Non-aqueous electrolyte is obtained bydissolving lithium hexafluorophosphate (LiPF₆) salt at a concentrationof 1.0 mol/L in a mixed solvent of EC (ethylene carbonate) and DEC(diethyl carbonate) in a volume ratio of 1:2.

A sheet of the positive electrode, a sheet of the negative electrode,and a sheet of separator made of a 20 μm-thick microporous polymer film(Celgard® 2320 commercially available from Celgard) interposed betweenthem are spirally wound using a winding core rod in order to obtain aspirally-wound electrode assembly. The wounded electrode assembly andthe electrolyte are then put in an aluminum laminated pouch in anair-dry room with dew point of −50° C., so that a flat pouch-typelithium secondary battery is prepared. The design capacity of thesecondary battery is 650 mAh when charged to 4.20 V. The non-aqueouselectrolyte solution is impregnated for 8 hrs at room temperature. Thebattery is pre-charged at 15% of its theoretical capacity and aged 1day, also at room temperature. The battery is then degassed using apressure of −760 mm Hg for 30 sec, and the aluminum pouch is sealed. Thebattery is prepared for use as follows: the battery is charged using acurrent of 0.2 C (with 1 C=650 mA) in CC mode (constant current) up to4.2V then CV mode (constant voltage) until a cut-off current of C/20 isreached, before being discharged in CC mode at 0.5 C rate down to acut-off voltage of 2.7V.

c) Cycle Life Experiments

The lithium secondary full cell batteries are charged and dischargedseveral times under the following conditions, both at 25° C. and 45° C.,to determine their charge-discharge cycle performance:

-   -   Charge is performed in CC mode under 1 C rate up to 4.2V, then        CV mode until C/20 is reached,    -   The cell is then set to rest for 10 min,    -   Discharge is done in CC mode at 1 C rate down to 2.7V,    -   The cell is then set to rest for 10 min,    -   The charge-discharge cycles proceed until the battery reaches        80% retained capacity. Every 100 cycles, the discharge is done        at 0.2 C rate in CC mode down to 2.7 V.

The retained capacity at the n^(th) cycle is calculated as the ratio ofthe discharge capacity obtained at cycle n to cycle 1.

d) XRD

XRD patterns are recorded on a Rigaku D/MAX 2200 PC X-ray diffractometerin the 17-144 2-theta range in a 0.02 degree scan step. Scan speed isset to 1.0 degree per minute. The goniometer with theta/2 theta BraggBrentano geometry has a radius of 185 mm. The copper target X-ray tubeis operated at KV and 40 mA. The diffracted beam monochromator, based ona curved graphite crystal, is used to remove KBeta Cu radiation. Thecollected XRD patterns comprise KAlpha Cu radiations with typicalwavelengths KAlpha₁=1.5405 Å and KAlpha₂=1.5443 Å in an IAlpha₂/IAlpha₁intensity ratio of ½ using a conventional scintillation counterdetector. The incident beam optic setup comprises a 10 mm divergentheight limiting slit (DHLS), a 1-degree divergence slit (DS) and 5degree vertical Soller slit. The diffracted beam optic setup includes a1-degree anti-scatter slit (SS), 5 degree vertical Soller slit and 0.3mm reception slit (RS). Crystallinity of the different materials iscalculated from the full width at half maximum (FWHM) of the (003) and(104) peaks where the hkl miller indices correspond to the O3-typehexagonal lattice with R-3m space group as defined by J. J. Braconnier,C. Delmas, C. Fouassier, and P. Hagenmuller, Mat. Res. Bull. 15, 1797(1980). FWHM is determined by further subtraction of the backgroundcontribution using the Sonnevelt-Visser's algorithm and KAlpha2elimination as implemented in the “Integral analysis v6.0” software fromRigaku between 17 and 20 2-theta and 43 and 43.5 2-theta for (003) and(104) peaks, respectively.

The FWHMs of the 015, 018, 110 and 113 reflections have been calculatedby local fitting of the experimental intensities Iobs. after KAlpha2elimination using pseudo-Voigt functions as follows:

${I_{{calc}.}\left( {2\theta} \right)} = {I_{0} + {\sum\limits_{i = 1}^{n}\; {I_{i}\left( {{{\mu_{i}\left( \frac{2}{\pi} \right)}\left( \frac{{FWHM}_{i}}{{4\left( {{2\theta} - {2\theta_{0,i}}} \right)^{2}} + {FWHM}_{i}^{2}} \right)} + {\left( {1 - \mu_{i}} \right)\frac{\sqrt{4{\ln (2)}}}{\sqrt{\pi}{FWHM}_{i}}^{({{- \frac{4{\ln {(2)}}}{{FWHM}_{i}^{2}}}{({{2\theta} - {2\theta_{0,i}}})}^{2}})}}} \right)}}}$

Where:

-   -   I₀ is the background level (in counts),    -   n is the number of diffracted peaks considered on the interval,    -   I_(i), μ_(i), 2θ_(0,i) and FWHM_(i) are respectively the height        of the pseudo-Voigt distribution (in counts),        Lorentzian-Gaussian mixing ratio, 2θ₀ position (in 2-theta        degrees) and FWHM (in 2-theta degrees) of peak i with i=1 . . .        n.

An example of such pseudo-Voigt fitting with n=3 peaks on the 63-702-theta range is shown on FIG. 15. 018, 110 and 113 peaks are wellfitted with square correlation coefficient R² in excess of 99.5%. Theauthors emphasize that FWHM determination in such conditions is atrivial operation and can be done with a large variety ofacademic/open/commercial software.

e) Material Hardness Evaluation

Materials hardness is estimated by means of particle size evolutionunder uni-axial stress as follows:

-   -   Cathode active material is put in a stainless-steel pellet die        and a uni-axial pressure of 100, 200 and 300 MPa is applied. The        obtained pellet is then gently unravelled with the finger to        obtain a loose powder for laser particle size distribution        measurement. The use of strong de-agglomeration methods such as        agate mortar is not suitable for this step as the particles        would be further broken and the fraction of fine particles would        be increased.    -   The laser particle size distribution is measured using a Malvern        Mastersizer 2000 with Hydro 2000MU wet dispersion accessory        after dispersing the powder in an aqueous medium. In order to        improve the dispersion of the powder in the aqueous medium,        sufficient ultrasonic irradiation, typically 1 minute for an        ultrasonic displacement of 12, and stirring are applied and an        appropriate surfactant is introduced.    -   a Hardness Strength Index (HIS) is defined as follows:

${{\Delta\Gamma}(P)} = {\frac{{\Gamma^{P}\left( {D\; 10_{P = 0}} \right)} - {\Gamma^{0}\left( {D\; 10_{P = 0}} \right)}}{\Gamma^{0}\left( {D\; 10_{P = 0}} \right)} \times 100\mspace{14mu} \left( {{in}\mspace{14mu} \%} \right)}$

where:

-   -   D10_(P=0) is the D10 value of the unconstrained powder (P=0        MPa),    -   Γ⁰(D10_(P=0)) is the cumulative volume particle size        distribution of the unconstrained powder at D10_(P=0). Note that        by definition Γ⁰(D10_(P=0)) always equals 10%.    -   Γ^(P)(D10_(P=0)) is the cumulative volume particle size        distribution of the pressed samples with P=100, 200 and 300 MPa        at D10_(P=0). This value can be determined by direct reading on        the plot or by local approximation using fitting functions.

An increase in the Γ^(P)(D10_(P=0)) value after the uni-axialcompression stress is direct evidence that particles have been brokeninto smaller particles. ΔΓ(P) is the relative increase ofΓ^(P)(D10_(P=0)) compared to Γ⁰(D10_(P=0)) and is expressed in %. Thechange in the Γ^(P)(D10_(P=0)) and ΔΓ(P) are therefore quantitativemeasures for determining the HSI of cathode powders according to theinvention. Such evolution of the cumulative particle size as function ofuniaxial stress is shown on FIG. 1, and more explicitly on FIG. 2 forExample 1 (see also below). In one embodiment, the powderous lithiummixed metal oxides according to the invention have a ΔΓ(P) value whichincreases by no more than 100%+(1−2a−b)×160% under 200 MPa, in anotherembodiment 150%+(1−2a−b)×160% under 300 MPa and in still anotherembodiment 125%+(1−2a−b)×100% under 300 MPa; where Ni³⁺ is the molarcontent on Ni³⁺ in the cathode materials, and a and b are the molarcontents of Mn and Co resp. in the cathode compoundLi_(1+x)[Ni_(1-a-b-c)M_(a)M′_(b)M″_(c)]_(1-x)O_(2-z).

f) Pressed Density

The pressed density is measured as follows: 3 grams of powder is filledinto a pellet die with a diameter “d” of 1.300 cm. A uniaxial load of2.8 tons, corresponding to a pressure of 207 MPa, is applied for 30seconds. After relaxing the load, the thickness “t” of the pressedpowder is measured. The pellet density is then calculated as follows:

3/(π×(d/2)² ×t) in g/cm³.

Also, the density of the powder under 300 MPa load is measured and givesinformation about the pressed density increase due to secondaryparticles breaking into smaller particles. In particular, smallerparticles increase the apparent density by filling the voids of thesecondary particles packing. The more the secondary particles break andcreate fines, the higher the density. This property is listed as densityat 300 MPa in the tables and is calculated as follows: 3/(π×(d/2)²×t) ing/cm³; where “d” is the diameter of the die (equal to 1.3 cm) and “t” isthe thickness of the pellet under 300 MPa load.

g) BET Specific Surface Area

The specific surface area is measured with the Brunauer-Emmett-Teller(BET) method using a Micromeritics Tristar 3000. 3 g of powder sample isvacuum dried at 300° C. for 1 h prior to the measurement in order toremove adsorbed species. The “true” BET is measured as follows: 10 g ofpowder sample is immerged in 100 g water and stirred for 10 mins at roomtemperature. The aqueous solution is then removed using Buchnerfiltration with suction. The washed powder is collected and dried at120° C. for 3 h. The true BET is then measured on the washed powderusing the same experimental conditions as ditto. The true BET isbelieved to be representative of the BET seen in the full cell once allLi-salts, such as LiOH, Li₂CO₃, Li₂SO₄, . . . have dissolved in theelectrolyte at potentials higher than 4V. In this case, preciousqualitative information is given on the microporosity of the particles;it is for example expected that the smaller the pores, the higher thetrue BET.

h) Residual Li₂CO₃ and LiOH Titration

The base content is a material surface property that can bequantitatively measured by the analysis of reaction products between thesurface and water. If powder is immersed into water a surface reactionoccurs. During the reaction the pH of the water increases (as basiccompounds dissolve) and the base is quantified by a pH titration. Theresult of the titration is the “soluble base content” (SBC). The contentof soluble base can be measured as follows: 100 ml of de-ionized wateris added to 20 g of cathode powder when Ni³⁺ content <0.4 and 4 g ofcathode powder when Ni³⁺ content ≧0.4, followed by stirring for 10minutes. The aqueous solution is then removed by using Buchnerfiltration with suction, thereby achieving >90 g of clear solution whichcontains the soluble base. The content of soluble base is titrated bylogging the pH profile during addition of 0.1 M HCl at a rate of 0.5ml/min until the pH reaches 3 under stirring. A reference voltageprofile is obtained by titrating suitable mixtures of LiOH and Li₂CO₃dissolved in low concentration in DI water. In almost all cases twodistinct plateaus are observed. The upper plateau with endpoint γ1 (inmL) between pH 8˜9 is OH⁻/H₂O followed by CO₃ ²⁻/HCO³⁻, the lowerplateau with endpoint γ2 (in mL) between pH 4˜6 is HCO³⁻/H₂CO₃. Theinflection point between the first and second plateau γ1 as well as theinflection point after the second plateau γ2 are obtained from thecorresponding minima of the derivative dpH/dVol of the pH profile. Thesecond inflection point generally is near to pH 4.7. Results are thenexpressed in LiOH and Li₂CO₃ weight percent as follows:

${{{Li}_{2}{CO}_{3}\mspace{14mu} {wt}\mspace{14mu} \%} = {\frac{73.8909}{1000} \times \left( {\gamma_{2} - \gamma_{1}} \right)}};$${{LiOH}\mspace{14mu} {wt}\mspace{14mu} \%} = {\frac{23.9483}{1000} \times {\left( {{2 \times \gamma_{2}} - \gamma_{1}} \right).}}$

i) ICP for Sulfur Titration

Sulfur content is measured using inductively coupled plasma atomicemission spectroscopy (ICP-OES) using an Agilent 720 series equipment.The analytic results are expressed in weight percent.

The invention is further illustrated in the following examples:

Example 1

The powderous cathode material of Example 1 (EX 1) is prepared by usinga conventional high temperature sintering. Li₂CO₃ (Chemetall) and aUmicore mass-produced metal oxy-hydroxide precursor with Ni/Mn/Co molarratio of 5/3/2 are mixed in a Li:M molar ratio of 1.01, resulting in thegeneral composition of Li_(1.005)Ni_(0.498)Mn_(0.299)Co_(0.199)O₂ orLi_(1.005)[Ni_(0.5)Mn_(0.3)Co_(0.2)]_(0.995)O₂. The mixture is reactedat a temperature of 910° C. for 10 hours using pilot-scale equipment.The sintered cake is then crushed and classified so as to obtain anon-agglomerated powder with a mean particle size D50 of 9.9 μm.Electrochemical and physical properties are shown on Tables 1 to 7.

Example 2

The powderous cathode material of Example 2 (EX 2) is prepared by usinga conventional high temperature sintering. Li₂CO₃ (Chemetall) and aUmicore mass-produced metal oxy-hydroxide precursor with Ni/Mn/Co molarratio of 5/3/2 are mixed in a Li:M molar ratio of 1.01, resulting in thegeneral composition of Li_(1.005)[Ni_(0.5)Mn_(0.3)Co_(0.2)]_(0.995)O₂.The mixture is reacted at a temperature of 930° C. for 10 hours usingpilot-scale equipment. The sintered cake is then crushed and classifiedso as to obtain a non-agglomerated powder with a mean particle size D50of 10 μm.

Electrochemical and physical properties are shown on Tables 1 to 7.

Counter Example 1

The powderous cathode material of Counter Example 1 (CEX 1) is preparedby using a conventional high temperature sintering. Li₂CO₃ (Chemetall)and a Umicore mass-produced metal oxy-hydroxide precursor with Ni/Mn/Comolar ratio of 5/3/2 are mixed in a Li:M molar ratio of 1.01, resultingin the general composition ofLi_(1.005)[Ni_(0.5)Mn_(0.3)Co_(0.2)]_(0.995)O₂. The mixture is reactedat a temperature of 950° C. for 10 hours using pilot-scale equipment.The sintered cake is then crushed and classified so as to obtain anon-agglomerated powder with a mean particle size D50 of 10 μm.

Electrochemical and physical properties are shown on Tables 1 to 7.

Example 3

The powderous cathode material of Example 3 (EX 3) is prepared by usinga conventional high temperature sintering. LiOH.H₂O (SQM) and a Umicoremass-produced metal oxy-hydroxide precursor with Ni/Mn/Co molar ratio of6/2/2 are mixed in a Li:M molar ratio of 1.01, resulting in the generalcomposition of Li_(1.005)Ni_(0.597)Mn_(0.199)Co_(0.199)O₂ orLi_(1.005)[Ni_(0.6)Mn_(0.2)Co_(0.2)]_(0.995)O₂. The mixture is reactedat a temperature of 860° C. for 10 hours using pilot-scale equipment.The sintered cake is then crushed and classified so as to obtain anon-agglomerated powder with a mean particle size D50 of 11.6 μm.Electrochemical and physical properties are shown on Tables 1 to 7.

Example 4

The powderous cathode material of Example 4 (EX 4) is prepared by usinga conventional high temperature sintering. Li₂CO₃ (Chemetall) and aUmicore mass-produced metal oxy-hydroxide precursor with Ni/Mn/Co molarratio of 6/2/2 are mixed in a Li:M molar ratio of 1.01, resulting in thegeneral composition of Li_(1.005)[Ni_(0.6)Mn_(0.2)Co_(0.2)]_(0.995)O₂.The mixture is reacted at a temperature of 870° C. for 10 hours usingpilot-scale equipment. The sintered cake is then crushed and classifiedso as to obtain a non-agglomerated powder with a mean particle size D50of 12.8 μm.

Electrochemical and physical properties are shown on Tables 1 to 7.

Counter Example 2

The powderous cathode material of Counter Example 2 (CEX 2) is preparedby using a conventional high temperature sintering. Li₂CO₃ (Chemetall)and a Umicore mass-produced metal oxy-hydroxide precursor with Ni/Mn/Comolar ratio of 6/2/2 are mixed in a Li:M molar ratio of 1.01, resultingin the general composition ofLi_(1.005)[Ni_(0.6)Mn_(0.2)Co_(0.2)]_(0.995)O₂. The mixture is reactedat a temperature of 890° C. for 10 hours using pilot-scale equipment.The sintered cake is then crushed and classified so as to obtain anon-agglomerated powder with a mean particle size D50 of 12.8 μm.

Electrochemical and physical properties are shown on Tables 1 to 7.

Examples 5, 6 and 7

These examples will demonstrate that the particle brittleness and cyclelife can be affected by modifying the Li:M composition. The powderouscathode material of Example 5, 6 and 7 (EX 5, 6 and 7) is prepared byusing a conventional high temperature sintering. A1203 powder, LiOH.H₂O(SQM) and a Umicore mass-produced Ni, Co oxy-hydroxide precursor with aNi/Co molar ratio of 84.2/15.8 are mixed in order to achieve a Ni/Co/Almolar ratio of 81.7/15.3/3.0 and Li:M equal to 0.98, 1.00 and 1.02 forEX5, EX6 and EX7, respectively. Heat treatment is conducted at atemperature of 775° C. for 10 hours under O₂ flow (4 m³/Kg) usinglaboratory-scale equipment. The sintered cakes are then crushed andclassified so as to obtain non-agglomerated powders with a mean particlesize D50 of approximately 12 to 13 μm. Electrochemical and physicalproperties are shown on Tables 1 to 7. Cross-sectional SEM and particleSEM are shown on FIG. 8.

Examples 8, 9 and 10

These examples will demonstrate that the particle brittleness and cyclelife can be affected by modifying the Li:M composition and dopantconcentration. The powderous cathode material of Example 8, 9 and 10 (EX8, 9 and 10) is prepared by using a conventional high temperaturesintering. A1203 powder, LiOH.H₂O (SQM) and an Umicore mass-producedNi—Co oxy-hydroxide precursor with a Ni/Co molar ratio of 84.2/15.8 aremixed in order to achieve a Ni/Co/Al molar ratio of 81.7/15.3/3.0 andLi:M equal to 0.98 and 1.00 for respectively EX8 and EX9 and a Ni/Co/Almolar ratio of 82.8/15.5/1.7 and Li:M equal to 1.00 for EX10. Heattreatment is conducted at a temperature of 775° C. for 10 hours under 02flow (4 m³/Kg) using pilot-scale equipment. The sintered cakes are thencrushed and classified so as to obtain non-agglomerated powders with amean particle size D50 of approximately 12 to 13 μm. Electrochemical andphysical properties are shown on Tables 1-7. Room temperature and 45° C.full cell performances are shown on FIGS. 11 and 12, respectively.Particle SEM's are shown on FIG. 13.

Examples 11, 12, 13, 14 and 15

200 g of cathode materials is prepared by mixing Li₂CO₃ (Chemetall) anda Umicore mass-produced metal oxy-hydroxide precursor with Ni/Mn/Comolar ratio of 5/3/2 in a Li:M molar ratio of 1.01 and reacting themixture at 910° C. for 10 hours using muffle furnace. The generalcomposition is Li_(1.010)Ni_(0.495)Mn_(0.297)Co_(0.198)O₂ orLi_(1.010)[Ni_(0.5)Mn_(0.3)Co_(0.2)]_(0.990)O₂.

The sintered cake is then crushed and 20 g of crushed product is sievedusing 270 mesh size sieve (53 μm opening) resulting in Example 11(EX11). The Dmax=D100 is 799.5 μm and the oversize fraction; determinedas the weight fraction of materials not going through the sieve is60.7%. The BET is 0.250 m²/g.

20 g of crushed product is grounded using a Cremania CG-01 150 W millfor 15 seconds resulting in Example 12 (EX12). The Dmax is 38.7 μm andthe oversize fraction; determined as the weight fraction of materialsnot going through the sieve is 9.0%. The BET is 0.299 m²/g.

20 g of crushed product is grounded using a Cremania CG-01 150 W millfor 30 seconds resulting in Example 13 (RX13). The Dmax is 38.2 μm andthe oversize fraction; determined as the weight fraction of materialsnot going through the sieve is 6.2%. The BET is 0.294 m²/g.

20 g of crushed product is grounded using a Cremania CG-01 150 W millfor 60 seconds resulting in Example 14 (EX14). The Dmax is 33.1 μm andthe oversize fraction; determined as the weight fraction of materialsnot going through the sieve is 4.4%. The BET is 0.343 m²/g.

20 g of crushed product is grounded using a Cremania CG-01 150 W millfor 300 seconds resulting in Example 15 (EX15). The Dmax is 32.0 μm andthe oversize fraction; determined as the weight fraction of materialsnot going through the sieve is 0.0%. The BET is 0.821 m²/g.

The physical properties of EX11 to EX15 are shown on Table 10. Thecrushed product EX11 has the lowest BET and the largest oversizefraction and largest Dmax value due to agglomerated particles. EX11 hasthe problem of offering low production throughput because of the largeoversize fraction and poor ability to make homogeneous electrodesbecause of large size agglomerates. EX11 is therefore unsuitable forapplication as lithium battery cathode materials and appropriatede-agglomeration is required.

EX12 to EX15 are prepared by increasing the milling time from 15 to 300seconds with the result that the oversize fraction and Dmax continuouslydecrease and the BET continuously increases. A decrease in oversizefraction is a positive effect as the production throughput is increased.The BET increase is however not desirable because the rate of parasitereactions with electrolyte increases. In particular, the authors expectthat the side reaction in EX15 will proceed about 2.4 times faster thanin EX14 because of the BET surface increase. Therefore, only a specialselection of milling conditions allow to control the Dmax, BET andoversize fraction within the embodiments of the present invention.

Discussion:

EX1, EX2 and CEX1

EX1, EX3 and CEX1 are in particular characterized by having differentΔΓ(P=300 MPa) values increasing from 83.7% for EX1, 116.4% for EX2 to266.4% for CEX1 (data in Table 3 that are derived from FIGS. 1 and 2 inthe case of EX1, for EX2 and CEX1 similar figures are obtained). Thisevolution of ΔΓ(P) indicates that more particles are broken into smallerparticles when applying a uniaxial stress of 200 MPa and 300 MPa in CEX1compared to EX1 and EX2.

Coin cell cycle life shows (in Table 1) that both the capacity fadingand energy fading at 4.5V are increasing from EX1, EX2 to CEX1. Inparticular, the improvement in cycle stability is more noticeable athigher charge/discharge 1 C and 1 C/1 C rates.

Full cell batteries using EX1, EX2 and CEX1 are fabricated as describedin the general description of experiments. Electrode densities of about3.20 g/cm³ are achieved for EX1, EX2 and CEX1, which is very close tothe density value of the powders when pressed under 208 MPa. Evolutionsof the retained capacity as function of cycle number are shown on FIG. 3at room temperature, and, on FIG. 4 at 45° C. (for each the top dottedline is for Ex1, the middle is for EX 2 and the bottom line is forCEX1). EX1 shows the best retention capacity with a retained capacitysuperior to 80% after 2000 cycles at room temperature and a retainedcapacity superior to 80% after 816 cycles at 45° C. (Table 5). Such ahigh retention capacity is particularly well-suited in the case ofapplications where long cycle life is required, such as electricalvehicles or grid storage. Comparatively, CEX1 demonstrates poor fullcell cycling performances.

Conclusion: the decrease of ΔΓ(P) at P=200 and 300 MPa fits very wellwith the decrease in coin cell fading at 4.5V and improvements of fullcell retention capacity upon cycling at both room temperature and 45° C.

Careful observation of SEM images (FIG. 5) shows that:

-   -   (i) The size of the primary particles is more developed in the        case of CEX1 (FIG. 5c ) compared to EX1 (FIG. 5a ). This is        consistent with the increase in the FWHM of the 003, 104, 015,        018, 110 and 118 which is attributed the smaller size of        coherent domains hence smaller size of primary particles (Table        7 & FIG. 14-15).    -   (ii) The density of nanometric voids and pores, typically 10-100        nm in size, is higher inside particles of CEX1 compared to EX1        and EX2. EX1, EX2 and CEX1 have similar BET values near 0.30        m²/g (Table 4). Their true BET are however very different and        substantially higher for EX1 and EX2 by about 0.50 m²/g compared        to CEX1. Presence of nanometric pores is then also expected in        EX1 and EX2 but with a much smaller characteristic size than in        CEX1 materials.

It is the author's opinion that the larger crystallinity and thepresence of internal porosity and voids with large concentration andlarge characteristic size, typically exceeding 10 nm in size, arefactors enhancing particle fracture and therefore making the particlesless resistant to uni-axial stress and more brittle upon electrochemicalcycling for CEX1 compared to EX1 and EX2. It is shown in the presentinvention that internal porosity of the particle can be controlled byprocess conditions and in this case by lowering the sinteringtemperature. As shown later in other examples, other suitable parametersinclude different Li:M ratio and different impurity content such aslithium salt based species that affect the stability of grain boundariesand therefore increase brittleness. For example, excessive amounts ofLiOH, Li₂CO₃ and Li₂SO₄ lead to accumulation of these species at thegrain boundaries, destabilization of the grain boundary and eventuallyincreased brittleness. In conclusion, EX1 and EX2 are embodiments of thepresent invention; CEX1 is a counter example.

EX3, EX4 and CEX2

Likewise, EX3, EX4 and CEX2 follow the same relationship between cyclestability and particle brittleness as EX1, EX2 and CEX1: the lower theΔΓ(P), the better the coin cell and full cell cycle life. In particular,EX3 is superior over 1400 cycles and over 1000 cycles at roomtemperature and 45° C., respectively (FIG. 6-7). The same inclusion ofvoids and grain boundary cracks within the particles are observed whenthe heat treatment temperature increases (FIG. 8-9). EX3, EX4 and CEX2however differentiate from EX1, EX2 and CEX1 in the larger amount ofeffective Ni³⁺, being 0.2 in EX1, EX2 and CEX1 and 0.4 in EX3, EX4 andCEX2. This higher Ni³⁺ content results in about 10 mAh/g higher CQ1 andDQ1 values compared to EX1, EX2 and CEX1. Residual LiOH and Li₂CO₃contents are also much increased. In particular, EX1 and EX3 havesimilar crystallinity as shown by the XRD FWHMs values but particles ofEX3 have a propensity to break more than EX1. As a result, coin cell andfull cell electrochemical properties of EX3 are inferior to EX1especially at room temperature. The better cycle life at 45° C. of EX3compared to EX1 might be explained by different surface chemistryregarding electrolyte oxidation due to the different Ni/Mn/Cocomposition and is not well understood by the authors; though theimprovements over EX4 and CEX2 are believed to be in relation with lowerbrittleness.

EX5, EX6 and EX7

EX5, EX6 and EX7 differ in their increasing Li:M ratio and as a resultdiffer in many properties. Strictly and as explained in theintroduction, the effective Ni³⁺ content increases with Li:M but in thepresent case the Ni³⁺ content will be considered constant and equal to0.817. Coin cell evaluation shown that DQ1 increases constantly withLi:M ratio but in the meantime both 0.1 C and 1 C Qfad and Efad aredegrading. Note that the 1 C/1 C cycle life at 4.5V does not allow todiscriminate products; the depth of charge and discharge, meaning theamount of Li reversibly extracted from the cathode materials being toohigh, which levels out differences. Residual LiOH and Li₂CO₃ contentsare also increasing with Li:M. Cross-sectional SEM (FIG. 10) shown thatthe density and the size of voids within the particles increases withLi:M. XRD FWHM values (Table 7) are also increasing with decreasingLi:M, meaning that crystallinity is decreasing with Li:M.

ΔΓ(P) hardness properties (Table 3) show a more complex behavior: asexpected from SEM and XRD, EX5 has the lowest ΔΓ(P) and the best coincell properties. EX6 and EX7 have larger ΔΓ(P) values than EX5, thoughbeing identical. A careful examination of the particle size distributionof EX7 reveals that the <3 μm volume fraction is circa 2% and higherthat EX5 and EX6. In fact though all the samples have close D50 between10˜14 μm, EX7 is the only example of this study to feature such highvalue of <3 μm fraction. The authors believe that these fine particlesare created during the post-treatment step of the powder and areevidence of a more brittle character of EX7 over EX6. As a conclusion,the increasing residual base content and the increasing crystallinitywith Li:M are resulting in larger particle brittleness for EX5, EX6 andEX7.

EX8, EX9 and EX10

EX8 and EX9 were an attempt to reproduce EX5 and EX6 at pilot scale,respectively, in order to measure full cell properties. Although thereexists a systematic offset in properties between EX8 and EX5 and EX9 andEX6, the differences between EX8 and EX9 are in line with the onereported for EX5 and EX6. EX8 shows significant improvements of 0.1 Cand 1 C Qfad and Efad coin cell fading compared to EX9 and there againalign well with the decrease of ΔΓ(P). Full cell cycle life is similarat room temperature but improved at 45° C. by about 10% more cyclesdemonstrated for EX8. See FIG. 11-12. Cross-sectional SEM is shown onFIG. 13.

EX10 has a lower Al and Co content compared to EX9 resulting in a higherNi³⁺ content. The ΔΓ(P) of EX10 is strongly increased over EX9 and the0.1 C and 1 C Qfad and Efad coin cell and the full cell room temperatureand 45° C. cycle stabilities are lowered.

TABLE 1 coin cell evaluation using schedule 1 (4.3-4.5-4.5 V/Li metal).Capacity and rate at 4.3 V Capacity and fading rate at 4.5 V (per 100cycles) Rate (per 0.1 C) QD7 QD8 QC1 QD1 Qirr 1 C 2 C 3 C 0.1 C 1 CCapacity fading (%) Energy fading (%) Sample mAh/g mAh/g % (%) (%) (%)mAh/g mAh/g 0.1 C 1 C 1 C/1 C 0.1 C 1 C 1 C/1 C Ex1 190.4 166.5 12.591.5 87.5 84.7 192.5 177.1 −2.4 1.1 18.1 −0.9 4.5 24.2 Ex2 191.3 170.610.8 92.0 88.4 86.0 195.2 180.9 1.0 5.2 20.1 2.3 9.2 26.6 CEX1 193.5170.4 11.9 91.7 88.0 85.6 195.2 180.0 4.8 9.5 24.1 6.3 13.9 31.3 EX3198.6 179.6 9.6 91.4 88.0 85.8 201.1 185.0 −0.5 2.8 14.5 0.5 5.0 18.7EX4 200.9 178.2 11.3 92.5 89.5 87.4 199.9 185.1 4.5 9.1 20.2 5.5 11.725.1 CEX2 200.0 178.2 10.9 92.0 88.9 86.8 200.4 185.6 3.9 9.8 21.4 5.112.8 26.7

TABLE 2 coin cell evaluation using schedule 2 (4.3-4.3-4.5 V/Li metal).Capacity and rate at 4.3 V Capacity and fading rate at 4.3 V and 4.5 V(per 100 cycles) Rate (per 0.1 C) Capacity fading (%) Energy fading (%)QC1 QD1 Qirr 1 C 2 C 3 C 1 C/1 C 1 C/1 C Sample mAh/g mAh/g % (%) (%)(%) 0.1 C 1 C (4.5 V) 0.1 C 1 C (4.5 V) EX5 221.1 188.1 14.9 92.5 89.486.8 2.6 7.6 22.3 3.6 9.0 27.7 EX6 221.3 194.7 12.0 91.7 88.9 87.4 6.38.8 23.6 6.5 9.4 28.6 EX7 221.3 195.8 11.5 92.7 89.9 88.5 9.8 12.9 23.410.0 13.7 27.7 EX8 220.7 190.1 13.9 91.7 88.4 85.6 −3.6 2.0 21.4 −2.53.2 26.7 EX9 222.5 194.7 12.5 80.2 89.6 87.6 0.7 5.9 17.8 1.5 6.8 22.4EX10 223.1 201.4 9.7 91.0 88.4 86.9 11.8 12.2 21.3 11.6 12.7 26.2

TABLE 3 brittleness properties. Li:M Ni³⁺ ΔΓ(P) ΔΓ(P) (1 + x)/ 1-2a-b P= 200 MPa P = 300 MPa (1) (2) (3) Sample (1 − x) a b (mol %) (%) (%) (%)(%) (%) EX1 1.010 0.3 0.2 0.200 56.4 83.7 132 182 145 EX2 1.010 0.3 0.20.200 83.8 116.4 132 182 145 CEX1 1.010 0.3 0.2 0.200 223.4 266.4 132182 145 EX3 1.010 0.2 0.2 0.400 78.5 112.9 164 214 165 EX4 1.010 0.2 0.20.400 122.8 184.2 164 214 165 CEX2 1.010 0.2 0.2 0.400 218.6 242.8 164214 165 EX5 0.980 0 0.183 0.817 68.4 97.4 230.72 280.72 206.7 EX6 1.0000 0.183 0.817 98.0 137.0 230.72 280.72 206.7 EX7 1.020 0 0.183 0.81791.2 135.5 230.72 280.72 206.7 EX8 0.985 0 0.183 0.817 77.9 109.4 230.72280.72 206.7 EX9 1.000 0 0.183 0.817 130.3 168.2 230.72 280.72 206.7EX10 1.000 0 0.172 0.828 174.0 219.3 232.48 282.48 207.8 (1) 100% +(1-2a-b) × 160% for P = 200 MPa (2) 150% + (1-2a-b) × 160% for P = 300MPa (3) 125% + (1-2a-b) × 100% for P = 300 Mpa

TABLE 4 physical properties. True Pressed Electrode Density at LiOHLi₂CO₃ S BET BET density density 300 MPa Sample wt % wt % wt % (m²/g)(m²/g) (g/cm³) (g/cm³) (g/cm³) EX1 0.12 0.06 0.1149 0.30 1.29 3.21 3.193.35 EX2 0.12 0.09 0.1129 0.37 1.49 — 3.21 3.44 CEX1 0.08 0.06 0.11230.28 0.93 3.28 3.19 3.61 EX3 0.33 0.16 0.1188 0.25 — 3.28 3.36 3.45 EX40.20 0.17 0.1179 0.32 — 3.40 3.30 3.50 CEX2 0.22 0.17 0.1497 — — 3.253.28 3.57 EX5 0.38 0.21 0.0517 0.28 2.15 — — 3.50 EX6 0.46 0.30 0.04990.30 2.21 — — 3.58 EX7 0.52 0.44 0.0491 0.34 2.51 — — 3.56 EX8 0.35 0.240.0508 0.24 1.76 3.40 3.41 3.49 EX9 0.37 0.24 0.0497 0.23 1.93 3.40 3.473.50 EX10 0.25 0.20 0.0503 0.28 — 3.46 3.51 3.84

TABLE 5 number of cycles to reach 80% retained capacity in full cell atroom temperature and 45° C. Sample RT cycle number 45° C. cycle numberEX1 >2000 816 EX2 1075 735 CEX1 938 614 EX3 1450 >1000 EX4 1230 567 CEX21139 567 EX5 — — EX6 — — EX7 — — EX8 1658 453 EX9 1681 409 EX10 1024 329

TABLE 6 Particle size distribution. Volume Volume fraction <1 fraction<3 D10 D50 D90 D99 D100 Sample μm (%) μm (%) (μm) (μm) (μm) (μm) (μm)EX1 0.0 0.0 5.6 9.9 17.4 24.6 32.3 EX2 0.0 0.0 5.6 10.0 17.6 25.2 33.3CEX1 0.0 0.0 7.1 12.4 21.5 30.3 38.2 EX3 0.0 0.0 6.4 11.7 20.6 29.2 38.5EX4 0.0 0.0 7.3 12.8 21.9 30.6 38.1 CEX2 0.0 0.0 8.1 14.4 24.9 34.8 45.1EX5 0.0 0.0 6.9 12.4 22.0 31.4 38.7 EX6 0.0 0.0 7.2 13.0 22.9 32.8 42.7EX7 0.6 2.0 6.9 12.8 22.6 32.2 38.8 EX8 0.0 0.0 7.1 12.9 22.7 32.4 39.6EX9 0.0 0.0 7.6 13.2 22.9 32.4 39.7 EX10 0.0 0.0 7.7 13.6 23.7 33.4 42.7

TABLE 7 FWHM and 2-theta position of 003, 104, 015, 018, 110 and 113peaks. Units are 2-theta degrees. 2θ FWHM 2θ FWHM 2θ FWHM 2θ FWHM 2θFWHM 2θ FWHM Sample 003 003 104 104 015 015 018 018 110 110 113 113 EX118.63 0.146 44.38 0.175 48.53 0.173 64.26 0.209 64.89 0.183 68.18 0.206EX2 18.65 0.140 44.40 0.165 48.55 0.162 64.28 0.206 64.92 0.174 68.210.196 CEX1 18.65 0.134 44.39 0.148 48.55 0.141 64.28 0.178 64.90 0.16168.19 0.171 EX3 18.69 0.192 44.45 0.180 48.62 0.171 64.39 0.212 64.980.198 68.28 0.217 EX4 18.67 0.140 44.44 0.163 48.61 0.154 64.38 0.19664.98 0.174 68.27 0.190 CEX2 18.68 0.136 44.44 0.155 48.61 0.150 64.380.191 64.97 0.170 68.26 0.186 EX5 18.72 0.140 44.49 0.158 48.67 0.14264.51 0.190 64.99 0.186 68.30 0.188 EX6 18.73 0.136 44.50 0.149 48.690.137 64.53 0.164 65.00 0.165 68.32 0.175 EX7 18.73 0.136 44.51 0.14448.69 0.132 64.54 0.155 65.02 0.156 68.34 0.162 EX8 18.71 0.141 44.490.160 48.67 0.150 64.50 0.191 65.00 0.189 68.31 0.195 EX9 18.73 0.13844.51 0.156 48.69 0.146 64.53 0.181 65.03 0.174 68.34 0.184 EX10 18.710.131 44.47 0.154 48.66 0.143 64.50 0.179 64.96 0.170 68.28 0.172

TABLE 8 coin cell schedule 1 used to evaluate EX1, EX2, EX3, EX4, CEX1and CEX2. 1 C definition is 160 mA/g. Cycle Charge Discharge number EndRest V/Li metal End Rest V/Li metal Type “n” C Rate Current (min) (V) CRate Current (min) (V) Part I: 1 0.10 — 30 4.3 0.10 — 30 3.0 Rate 2 0.250.05 C 10 4.3 0.20 — 10 3.0 performance 3 0.25 0.05 C 10 4.3 0.50 — 103.0 4 0.25 0.05 C 10 4.3 1.00 — 10 3.0 5 0.25 0.05 C 10 4.3 2.00 — 103.0 6 0.25 0.05 C 10 4.3 3.00 — 10 3.0 Part II: 7 0.25  0.1 C 10 4.50.10 — 10 3.0 1 C cycle life 8 0.25  0.1 C 10 4.5 1.00 — 10 3.0  9~330.50  0.1 C 10 4.5 1.00 — 10 3.0 34  0.25  0.1 C 10 4.5 0.10 — 10 3.035  0.25  0.1 C 10 4.5 1.00 — 10 3.0 Part III: 36~60 1.00 — 10 4.5 1.00— 10 3.0 1 C/1 C cycle life

TABLE 9 coin cell schedule 2 used to evaluate EX5, EX6, EX7, EX8, EX9and EX10. 1 C definition is 160 mA/g. Cycle Charge Discharge number EndRest V/Li metal End Rest V/Li metal Type “n” C Rate Current (min) (V) CRate Current (min) (V) Part I: 1 0.10 — 30 4.3 0.10 — 30 3.0 Rate 2 0.250.05 C 10 4.3 0.20 — 10 3.0 performance 3 0.25 0.05 C 10 4.3 0.50 — 103.0 4 0.25 0.05 C 10 4.3 1.00 — 10 3.0 5 0.25 0.05 C 10 4.3 2.00 — 103.0 6 0.25 0.05 C 10 4.3 3.00 — 10 3.0 Part II: 7 0.25  0.1 C 10 4.30.10 — 10 3.0 1 C cycle life 8 0.25  0.1 C 10 4.3 1.00 — 10 3.0  9~330.50  0.1 C 10 4.3 1.00 — 10 3.0 34  0.25  0.1 C 10 4.3 0.10 — 10 3.035  0.25  0.1 C 10 4.3 1.00 — 10 3.0 Part III: 36~60 1.00 — 10 4.5 1.00— 10 3.0 1 C/1 C cycle life

TABLE 10 physical properties of EX11 to EX15. D50 D99 D100 wt % oversizeBET Sample (μm) (μm) (μm) (wt %) (m²/g) EX11 18.1 544.2 799.5 60.7%0.250 EX12 12.4 31.2 38.7 9.0% 0.299 EX13 12.1 30.0 38.2 6.2% 0.294 EX1410.9 26.5 33.1 4.4% 0.343 EX15 10.2 23.9 32.0 0.0% 0.821

1-17. (canceled)
 18. A powderous positive electrode material for alithium secondary battery, the material having the general formulaLi_(1+x)[Ni_(1-a-b-c)M_(a)M′_(b)M″_(c)]_(1−x)O_(2-z); M being either oneor more elements selected from the group consisting of Mn, Zr and Ti, M′being either one or more elements selected from the group consisting ofAl, B and Co, M″ being a dopant different from M and M′, x, a, b and cbeing expressed in mol with −0.02≦x≦0.02, 0≦c≦0.05, 0.10≦(a+b)≦0.65 and0≦z≦0.05; and wherein the powderous material is characterized by havinga BET value ≦0.37 m²/g, a D_(max)<50 μm, and a hardness strength indexΔΓ(P) of no more than 100%+(1−2a−b)×160% for P=200 MPa, wherein${{\Delta\Gamma}(P)} = {\frac{{\Gamma^{P}\left( {D\; 10_{P = 0}} \right)} - {\Gamma^{0}\left( {D\; 10_{P = 0}} \right)}}{\Gamma^{0}\left( {D\; 10_{P = 0}} \right)} \times 100\mspace{14mu} \left( {{in}\mspace{14mu} \%} \right)}$with D10_(P=0) being the D10 value of the unconstrained powder (P=0MPa), Γ⁰(D10_(P=0)) being the cumulative volume particle sizedistribution of the unconstrained powder at D10_(P=0), andΓ^(P)(D10_(P=0)) being the cumulative volume particle size distributionat D10_(P=0) of the pressed samples with P being expressed in MPa. 19.The powderous positive electrode material of claim 18, wherein M′=Mn andM″ comprises either one of Al or Co.
 20. The powderous positiveelectrode material of claim 18, wherein ΔΓ(P)≦150%+(1−2a−b)×160% forP=300 MPa.
 21. The powderous positive electrode material of claim 18,wherein ΔΓ(P)≦125%+(1−2a−b)×100% for P=300 MPa.
 22. The powderouspositive electrode material of claim 18, wherein either: ΔΓ(P)≦180% forP=300 MPa, or ΔΓ(P)≦140% for P=300 MPa, or ΔΓ(P)≦100% for P=300 MPa. 23.The powderous positive electrode material of claim 18, wherein 1−a−b≧0.5and 1+x<1.
 24. The powderous positive electrode material of claim 18,having a BET value after wash >1 m²/g.
 25. The powderous positiveelectrode material of claim 18, having a pressed density greater than3.0 g/cm³.
 26. The powderous positive electrode material of claim 18,comprising up to 2 mol % of W, Mo, Nb, Zr, or a rare earth element. 27.The powderous positive electrode material of claim 18, having a solublebase content (Li₂CO₃+LiOH)<0.8 wt %.
 28. The powderous positiveelectrode material of claim 18, comprising secondary particlessubstantially free from porosities larger than 20 nm.
 29. The powderouspositive electrode material of claim 18, comprising secondary particlescontaining less than 20 voids larger than 20 nm.
 30. The powderouspositive electrode material of claim 18, having a FWHM value of the(104) peak as defined by the pseudo hexagonal lattice with R-3m spacegroup which is greater than 0.125 2-theta degrees.
 31. The powderouspositive electrode material of claim 18, having a FWHM value of the(015) peak as defined by the pseudo hexagonal lattice with R-3m spacegroup which is greater than 0.125 2-theta degrees.
 32. The powderouspositive electrode material of claim 18, having a FWHM value of the(113) peak as defined by the pseudo hexagonal lattice with R-3m spacegroup which is greater than 0.16 2-theta degrees.
 33. The powderouspositive electrode material of claim 18, having a second phaseLiN_(x′)O_(y′) with 0<x′<1 and 0<y′<2, where N is selected from thegroup consisting of either one or more of W, Mo, Nb, Zr and rare earthelements.
 34. A method for preparing the powderous positive electrodematerial according to claim 18, the material having the general formulaLi_(1+x)[Ni_(1-a-b-c)M_(a)M′_(b)M″_(c)]_(1−x)O_(2-z), the methodcomprising: providing a mixture of one or more precursor materialscomprising either one or more of Ni, M, M′ or M″, and a precursormaterial comprising Li, sintering the mixture at a temperature Texpressed in ° C., with (945−(248*(1−2a−b)≦T≦(985−(248*(1−2a−b)),thereby obtaining agglomerated particles, and pulverizing theagglomerated particles whereby a powder is obtained having a BET≦0.37m²/g and a D_(max)<50 μm.